High frequency and wide band impedance matching via

ABSTRACT

A high frequency and wide band impedance matching via is provided. As an application to multi-layer printed circuit boards, for example, the multi-layer circuit board has several signal transmission traces, several ground layers, signal transmission vias and ground vias. The signal transmission traces and the ground layers are sited on different circuit layers, and each signal transmission trace is opposite to one of the ground layers. The signal transmission vias are connected between the signal transmission traces. The ground vias are connected between the ground layers. The ground vias are opposite to the signal transmission vias, and the ground vias corresponding to the signal transmission vias are sited to stabilize the characteristic impedance of the transmission traces.

BACKGROUND

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 94101223 filed in Taiwan on Jan. 14,2005, the entire contents of which are hereby incorporated by reference.

FIELD OF INVENTION

The invention relates to a conductive via to be applied to severalsubstrates, such as multi-layer circuit boards, low temperature co-firedceramics (LTCCs), integrated circuits (ICs), thick-film ceramics,thin-film ceramics or silicon-on-glass substrate processes, and moreparticular, to a high frequency and wide band impedance matching via.

DESCRIPTION OF THE RELATED ART

In products related to electronic systems, such as the multi-layercircuit boards, LTCCs, ICs, thick-film ceramics, thin-film ceramics andsilicon-on-glass substrate processes, the printed circuit board (PCB),which supports electronic components generally, is a plan substratewhich was made up of glass fibers and on which conductive circuitry wasprinted. With the prevailing trend in electronic products being ‘slimtype’ and ‘mini size’, the development of the PCB is inclined to the onewith a small-bore diameter, high density, multi-layer and thin circuit.An excellent scheme of increasing the density of the circuit is themulti-layer circuit board.

Once the number of layers of the PCB is increased, it results suchserious interference that signal transmission lines must be through eachlayer. Further, since the prevailing trend in electronic products ishigh frequency, high transmission speed and a higher requirement foraccuracy of the transmission impedance and efficiency of the signaltransmission, the impedance dis-matching results in the signal bounce tocause many problems. In light cases, the system will work unstable, andin serious cases, the system will be damaged. In consequence, thecircuitry design for the PCB is aimed at its width and distance of thesignal transmission lines, further, at setting up the balanced impedancedesign. However, the circuitry design for the conventional PCB ischiefly and simply aimed at the signal transmission in a plane and notaimed at the signal transmission in a perpendicular. A difficult pointof the circuitry design for the multi-layer circuit board is the signaltransmission between the different layers in a perpendicular direction,so it will avoid vertically transmitting the signals over the viasbetween the layers in a perpendicular direction in many high-frequencycircuitry designs.

In the U.S. patent application of publication No. 2004/0053014, amultilayer printed board is introduced. It has first and second signaltransmission lines and first and second ground layers. A signal via isconnected between the first and second transmission lines. Ground viasare connected between the first and second ground layers, and they arenear to the signal via but not connected with it. The end of the firstground layer protrudes with respect to the second ground layer andextends nearer to the signal via than the second ground layer. Thus, itis possible to stabilize the characteristic impedance of the firsttransmission line. Further, the first and second ground layers areinterlaced, so that it is procured to control the characteristicimpedance effectively. However, this circuitry design is complicated, sothat flexibility in circuit application is decreasing and precisioncontrol of its PCB is not easy.

SUMMARY

Accordingly, the present invention is directed to a high frequency andwide band impedance matching via, to substantially solve the problems inthe prior art. As an application to multi-layer printed circuit boards,for example, signal transmission traces sited on the different circuitlayers are connected by vertical signal transmission vias, and verticalground vias corresponding to the vertical signal transmission vias aresited to stabilize the characteristic impedance of the signaltransmission traces, so that electrical signals having high frequencyand high speed are completely transmitted in three-dimensional space.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, a highfrequency and wide band impedance matching via, which is applied to eachsubstrate, comprises a first signal transmission trace, a second signaltransmission trace, a signal via, a first ground layer, a second groundlayer and a ground via, wherein the signal and the ground vias aresubstantially perpendicular to the first and the second signaltransmission traces and the first and the second ground layers. Thefirst and the second signal transmission traces are sited on differentsurface of the circuit layer respectively. Moreover, the first signaltransmission trace is connected to the second signal transmission traceby the signal via, which is sited within the substrate, and the groundvia is sited adjacent to the signal via. Moreover, the first and thesecond ground layers are opposite to the first and the second signaltransmission traces, respectively, and connected by the ground via. Theimpedance is controlled by adjusting the distance between the ground viaand the signal via, thereby enabling the signal transmission of thesignal via, to have matching impedance. More preferably, the length ofthe signal via is similar to that of the ground via.

The structure has two ground vias, which are symmetrically sited aroundthe signal via to be similar to a coplanar waveguide, and further, thestructure has at least two ground vias which are symmetrically sitedaround the signal via to be similar to a coaxial cable. Furthermore,each ground via is connected to another by a conductor portion, therebypromoting electric characteristics of the structure.

To match different circuitry design, the invention is applied in thesignal transmission for differential pairs. The structure comprises afirst signal transmission differential pair, a second signaltransmission differential pair, a pair of signal vias, plane conductortraces and several ground vias, wherein the pair of ground vias aresubstantially perpendicular to the first and the second signaltransmission differential pairs. The first and the second signaltransmission differential pairs are respectively sited on two surfacesof the substrate, and the first and the second signal transmissiondifferential pairs are connected by the pair of signal vias. The groundvias are connected to each other, and they are adjacent to the signalvias at a distance and are symmetrically sited in the insulation layerto match the signal vias. More preferably, the length of the signal viais similar to that of the ground via.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood from the detaileddescription given hereinbelow illustration only and thus does not limitthe present invention, wherein:

FIG. 1A and FIG. 1B are schematic views showing cross-sections of firstand second embodiments according to the invention, respectively;

FIG. 2 is a schematic view showing a cross-section of a third embodimentaccording to the invention;

FIG. 3A, FIG. 3B, FG. 3C and FIG. 3D are perspectives showingthree-dimensional structures of fourth, fifth, sixth and seventhembodiments according to the invention, respectively;

FIG. 4A is a schematic view showing a three-dimensional structure of aeighth embodiment according to the invention;

FIG. 4B is a chart showing the measurements of impedance distribution ofthe three-dimensional structure in FIG. 4A;

FIG. 5A and FIG. 5B are schematic views showing a three-dimensionalstructure of ninth and tenth embodiments according to the invention,respectively;

FIG. 5C and FIG. 5D are perspectives showing a three-dimensionalstructure of eleventh and twelfth embodiments according to theinvention, respectively;

FIG. 6A is a schematic view showing a three-dimensional structure of anthirteenth embodiment according to the invention; and

FIG. 6B are perspectives showing a three-dimensional structure of afourteenth embodiment according to the invention.

DETAILED DESCRIPTION

A conductive through-via according to the invention is applied to allkinds of substrates, such as multi-layer circuit boards, low temperatureco-fired ceramics (LTCCs), integrated circuits (ICs), thick-filmceramics, thin-film ceramics or silicon-on-glass substrate processes,and has ground vias sited around signal vias, thereby enabling thesignal transmission of the signal vias to have impedance match. As anapplication to multi-layer printed circuit boards, for example, adetailed structure is described below. The objective of the multi-layerprinted circuit board with the impedance matching is achieved through adesign of the structure. The structure of the multi-layer printedcircuit board is a combination of insulation layers and circuit layers,which are stacked in repeating order of each other, in where circuitlayers are electrically connected to another one by vertical signalvias, and vertical ground vias are sited appropriately, to enable thesignal transmission of the signal vias to achieve impedance match.

In an embodiment, the multi-layer printed circuit board is a combinationof several insulation layers and several circuit layers, which arestacked staggeredly. Refer to FIG. 1A, which is a cross-section of afirst embodiment according to the invention. A six-layer printed circuitboard, for example, has six circuit layers 110, which are separated byinsulation layers 120. The circuit layer 110 may be a signaltransmission trace or a ground layer. The signal and the ground vias113, 114 are substantially perpendicular to first and second signaltransmission traces 111, 112, and first and second ground layers 115,116. The first signal transmission trace 111 is sited on the bottomcircuit layer 110, as a first surface of the substrate, the secondsignal transmission trace 112 is sited on the top circuit layer 110, asa second surface of the substrate, and the several insulation layers 120separate them. The first signal transmission trace 111 is connected tothe second signal transmission trace 112 by the signal via 113, and theground via 114 sited adjacent to the signal via 113 runs throughinternal circuit layers and is at a distance D from the signal via 113.Herein, the ground via 114 connects the first ground layer 115 with thesecond ground layer 116. In other words, the first signal transmissiontrace 111 is opposite to the first ground layers 115, the second signaltransmission trace 112 is opposite to the second ground layers 116, andthe signal via 113 is opposite to the ground via 114. Thus the impedanceis controlled through adjusting the distance D, so that the signaltransmission of the signal vial 13 has impedance match. More preferably,the length of the ground via 114 is similar to that of the signal via113, and the ground via 114 is not connected to the first and secondsignal transmission traces 111, 112, as shown in FIG. 1B.

In another embodiment, several ground vias are symmetrically sitedaround the signal via to form a structure similar to a coplanarwaveguide. FIG. 2 illustrates a cross-section of a structure accordingto a third embodiment. Referring to FIG. 2, a six-layer printed circuitboard, for example, has six circuit layers 110, which are separated byinsulation layers 120, where the circuit layer 110 may be a signaltransmission trace or a ground layer. The structure according to thesecond embodiment of the invention comprises a first signal transmissiontrace 111, a second signal transmission trace 112, a signal via 113 andtwo ground vias 114, wherein the signal and the ground vias 113, 114 aresubstantially perpendicular to the first and the second signaltransmission traces 111, 112, and first and second ground layers 115,116. The first and the second signal transmission trace 111, 112 arerespectively sited on the bottom and top circuit layer 110, and theseveral insulation layers 120 separate them. The first signaltransmission trace 111 is connected to the second signal transmissiontrace 112 by the signal via 113, and the ground vias 114 sited adjacentand symmetrical to the signal via 113 run through internal circuitlayers 110 and are at a distance D from the signal via 113. Herein, theground vias 114 connect the first ground layer 115 with the secondground layer 116. In other words, the first signal transmission trace111 is opposite to the first ground layer 115, the second signaltransmission trace 112 is opposite to the second ground layer 116, andthe signal via 113 is opposite to the ground vias 114. Thus theimpedance is controlled thought adjusting the distance D, so that thesignal transmission of the signal via 113 has impedance match. Thestructure further comprises at least one conductor portion (not showedin the drawing). The ground vias are connected by the conductor portionsited around the signal via 113 and are separated from the signal via113. The conductor portion is the cambered conductor portion or a hollowconductor portion. The form of the hollow conductor portion is circular,such as a substantial circular form, a rectangle, etc. In this case, thenumber of ground vias is two. However, it can be more than two accordingto the invention. More preferably, the length of the signal via is alsosimilar to that of the ground via (not shown to convenientlyillustrate).

Further, the structure according to the invention is applied in thesignal transmission for differential pairs. Refer to FIG. 3A, which isthree-dimensional structures of a fourth embodiment according to theinvention. In this embodiment, the structure comprises a first signaltransmission differential pair 311, a second signal transmissiondifferential pair 312, a pair of signal vias, several ground vias 314and a conductor portion. In this case, the conductor portion is a hollowconductor portion 316. The pair of ground vias 314 is substantiallyperpendicular to the first and the second signal transmissiondifferential pairs 311, 312. The first and the second signaltransmission differential pairs 311, 312 are separated with aninsulation layer 320, and the first and the second signal transmissiondifferential pairs 311, 312 are connected by several signal vias. Thesignal vias comprise several vertical signal vias 313 and several planeconductor traces 315. The vertical signal vias 313 are intersected inthe insulation layer 320, to form a vertically electrical connection,and the plane conductor traces 315 are connected to the vertical signalvias 313 to form an electrical connection in the plane. The ground vias314 are adjacent to the signal vias and are symmetrically sited in anopposite position of the signal vias and in the insulation layer 320, tomatch the vertical signal vias 313. The ground vias 314 are electricallyconnected by the hollow conductor portion 316.

The hollow conductor portion 316 surrounds the vertical signal vias 313,as shown in FIG. 3A; and further, the conductor portion 317 is acambered conductor portion sited in one side of the vertical signal vias313, as shown in FIG. 3B. Herein, the signal via 313 is opposite to theground via 314, and the length of the signal via 313 is preferablysimilar to that of the ground via 314.

In fact, the first signal transmission differential pair 311 may beopposite to the first ground layer 317, and the second signaltransmission differential pair 312 may be opposite to the second groundlayer 318, and the first and second ground layers 317, 318 are connectedto the hollow conductor portion 316, as shown in FIG. 3C and FIG. 3D.That is, the first and second ground layers 317, 318 are connected toeach other by the ground vias 314. In this case, although the first andsecond ground layers 317, 318 are traces in FIG. 3C and FIG. 3D, theymay be whole planes according to actual requirement for circuit design.

To describe the invention more clearly, a six-layer printed circuitboard is simulating the experiment of a high-frequency electromagneticeffect. Assume that the depth of each insulation layer is tenmilli-inches (mil), the depth of the circuit layer is one milli-inch(mil), the diameter of the conductor portion is twenty milli-inches(mil), the total length of the transmission trace is two hundredsmilli-inches (mil), and the material of the insulation layer isfiberglass FR4 (DK=4.2 and DF=0.03) The description of a schematic view,showing a three-dimensional structure and the stimulated result thereof,follows.

Refer to FIG. 4A, the structure comprises a first signal transmissiontrace 411, a second signal transmission trace 412, a signal via 413, andtwo ground vias 414. The signal and the ground vias 413, 414 aresubstantially perpendicular to the first and the second signaltransmission traces 411, 412. The first and the second signaltransmission traces 411, 412 are separated with an insulation layer (notshown to conveniently illustrate), and the first and the second signaltransmission traces 411, 412 are connected by the signal via 413. Theground vias 414 are sited adjacent to the signal via 413 at a distance Dand are symmetrically sited on the side of the signal via 413. Herein,first ground layer 416 is opposite to the first signal transmissiontrace 411, e.g. above the first signal transmission trace 411, and it isconnected to the ground vias 414. Moreover, second ground layer 417 isopposite to the second signal transmission trace 412, e.g. under thesecond signal transmission trace 412, and it is connected to the groundvias 414. Furthermore, the signal vias 413 is opposite to the groundvias 414, and the length of the signal via 413 is preferably similar tothat of the ground vias 414.

Refer to FIG. 4B, which is a schematic view of impedance distribution ofthe stimulated result, wherein the transverse axis represents impedance(Z) and vertical axis represents time (T). In FIG. 4B, Line 1 representsthe 50 ohm transmission line, Line 2 represents the impedancetransmission when the first ground layer opposite to the first signaltransmission trace is not connected to the second ground layer isopposite to the second signal transmission trace, Line 3 represents theimpedance transmission when the connection between the first groundlayer opposite to the first signal transmission trace and the secondground layer is opposite to the second signal transmission trace is at adistant place, Line 4 represents the impedance transmission when thereis a ground via opposite to the signal via and the ground via connectsthe first ground layer with the second ground layer, Line 5 representsthe impedance transmission when there are a pair of the ground viasopposite to and symmetrically around the signal via and the ground viasconnect the first ground layer with the second ground layer, and Line 6represents the impedance transmission when there are a pair of theground vias opposite to and symmetrically around the signal via, theground vias connect the first ground layer with the second ground layerand there are a pair of circular conductor portions connecting theground vias.

Contrasted with the same structure without ground vias and thestructures of the first stimulated embodiment having a different Dvalue, the structure without ground vias has the most dis-matchingimpedance and its maximum discrepancy is 40.1%. The maximum discrepancyof the matching impedance in the structures of the first stimulatedembodiment, of which the distance between the ground via and the signalvia is 10 mils (i.e. D=10 mils) is 9.5%. The maximum discrepancy of thematching impedance in the structures of the first stimulated embodiment,of which the distance between the ground via and the signal via is 15mils (i.e. D=15 mils) is 5.3%. According to the result, the dis-matchingimpedance of the structure is effectively improved by applying theinvention and the better impedance match is acquired by adjusting thedistance between the ground via and the signal via.

Further, the ground vias are connected to each other by conductorportions. Refer to FIG. 5A, the structure comprises a first signaltransmission trace 411, a second signal transmission trace 412, a signalvia 413, two ground vias 414 and two circular conductor portions 415.The signal and the ground vias 413, 414 are substantially perpendicularto the first and the second signal transmission traces 411, 412. Thefirst and the second signal transmission traces 411, 412 are separatedwith an insulation layer (not shown to conveniently illustrate), and thefirst and the second signal transmission traces 411, 412 are connectedby the signal via 413. The ground vias 414 are sited adjacent to thesignal via 413 and symmetrically sited on the side of the signal via413. Moreover, the ground vias 414 are electrically connected by thecircular conductor portions 415. On the other hand, the structure, whichis similar to a coaxial cable, has a plurality of ground vias 414symmetrically sited around the signal via 413, as shown in FIG. 5B.Herein, first ground layer 416 is opposite to the first signaltransmission trace 411, e.g. above the first signal transmission trace411, and it is connected to the ground vias 414. Moreover, second groundlayer 417 is opposite to the second signal transmission trace 412, e.g.under the second signal transmission trace 412, and it is connected tothe ground vias 414, as shown in FIG. 5C and in FIG. 5D. Further, eachof the first and second ground layers 416, 417 may be connected to thecircular conductor portion 415, as shown in FIG. 5E. Furthermore, thelength of the signal via 13 is preferably similar to that of the groundvias 414. In this case, although the first and second ground layers 416,417 are whole planes in FIG. 5C and FIG. 5D, they may be tracesaccording to actual requirement for circuit design.

Furthermore, the conductor portions are semicircular, as shown in FIG.6A. Refer to FIG. 6A, the structure comprises a first signaltransmission trace 411, a second signal transmission trace 412, a signalvia 413, two ground vias 414, two circular conductor portions 415 andtwo semicircular conductor portions 416. The signal and the ground vias413, 414 are substantially perpendicular to the first and the secondsignal transmission traces 411, 412. The first and the second signaltransmission traces 411, 412 are separated by an insulation layer (notshown to conveniently illustrate), and the first and the second signaltransmission traces 411, 412 are connected by the signal via 413. Theground vias 414 are sited adjacent to the signal via 413 andsymmetrically sited on the side of the signal via 413. The ground vias414 are electrically connected by the circular conductor portions 415.Moreover, the tops and the bottoms of the ground vias 414 areelectrically connected by the semicircular conductor portions 416respectively. Further, first ground layer 416 is opposite to the firstsignal transmission trace 411, e.g. above the first signal transmissiontrace 411, and it is connected to the ground vias 414. Moreover, secondground layer 417 is opposite to the second signal transmission trace412, e.g. under the second signal transmission trace 412, and it isconnected to the ground vias 414, as shown in FIG. 6B. Further, althoughthe first and second ground layers 416, 417 are whole planes in FIG. 6B,they may be traces according to actual requirement for circuit design,and each of they may be connected to the circular conductor portionconnecting the ground vias. Furthermore, the length of the signal via 13is preferably similar to that of the ground vias 414.

Certain variations would be apparent to those skilled in the art, whichvariations are considered within the spirit and scope of the claimedinvention.

1. A high frequency and wide band impedance matching via, comprising: afirst signal transmission trace; a first ground layer opposite to thefirst signal transmission trace; a second signal transmission trace; asecond ground layer opposite to the second signal transmission trace; asignal via substantially perpendicular to the first and the secondsignal transmission traces for connecting the first signal transmissiontrace with the second signal transmission trace; and at least one groundvia opposite to the signal via and adjacent to the signal via forconnecting the first ground layer with the second ground layer.
 2. Theimpedance matching via of claim 1, wherein a length of the signal via ispreferably similar to a length of the ground via.
 3. The impedancematching via of claim 1, wherein a plurality of the ground vias aresymmetrically sited around the signal via.
 4. The impedance matching viaof claim 1, further comprising: at least one conductor portion forconnecting the ground vias.
 5. The impedance matching via of claim 4,wherein the conductor portion surrounds the signal via.
 6. The impedancematching via of claim 4, wherein the conductor portion is connected tothe ground vias and around a side of the signal via.
 7. A high frequencyand wide band impedance matching via applied to a substrate which has afirst surface and a second surface opposite to each other, comprising: afirst signal transmission differential pair sited on the first surfaceof the substrate; a second signal transmission differential pair sitedon the second surface of the substrate; a pair of signal vias sited inthe substrate and substantially perpendicular to the first and thesecond signal transmission differential pairs for connecting the firstsignal transmission differential pair with the second signaltransmission differential pair; and a plurality of ground viassubstantially perpendicular to the first and the second signaltransmission differential pairs, symmetrically adjacent to the signalvias and connected to each other.
 8. The impedance matching via of claim7, wherein a length of the signal via is preferably similar to a lengthof the ground via.
 9. The impedance matching via of claim 7, furthercomprise: at least one plane conductor trace connected to the verticalsignal vias to form an electrical connection.
 10. The impedance matchingvia of claim 7, further comprising: at least one conductor portion forconnecting the ground vias.
 11. The impedance matching via of claim 10,wherein the conductor portion is a hollow conductor portion.
 12. Theimpedance matching via of claim 10, wherein the conductor portionsurrounds the signal via.
 13. The impedance matching via of claim 10,wherein the conductor portion is connected to the ground vias and arounda side of the signal via.
 14. The impedance matching via of claim 7,further comprise: a first ground layer opposite to the first signaltransmission differential pair; and a second ground layer opposite tothe second signal transmission differential pair; wherein the groundvias connect the first ground layer with the second ground layer.